Merge branch 'da-fix-n-plus-1-query-on-starrers-list' into 'master'

Fix N+1s queries while loading users on the project starrers list

See merge request gitlab-org/gitlab-ce!31984

app/controllers/projects/starrers_controller.rb

@@ -5,11 +5,11 @@ class Projects::StarrersController < Projects::ApplicationController
 
   def index
     @starrers = UsersStarProjectsFinder.new(@project, params, current_user: @current_user).execute
+    @sort = params[:sort].presence || sort_value_name
+    @starrers = @starrers.preload_users.sort_by_attribute(@sort).page(params[:page])
     @public_count  = @project.starrers.with_public_profile.size
     @total_count   = @project.starrers.size
     @private_count = @total_count - @public_count
-    @sort = params[:sort].presence || sort_value_name
-    @starrers = @starrers.sort_by_attribute(@sort).page(params[:page])
   end
 
   private

app/models/users_star_project.rb

@@ -17,6 +17,7 @@ class UsersStarProject < ApplicationRecord
   scope :by_project, -> (project) { where(project_id: project.id) }
   scope :with_visible_profile, -> (user) { joins(:user).merge(User.with_visible_profile(user)) }
   scope :with_public_profile, -> { joins(:user).merge(User.with_public_profile) }
+  scope :preload_users, -> { preload(:user) }
 
   class << self
     def sort_by_attribute(method)

spec/controllers/projects/starrers_controller_spec.rb

@@ -32,6 +32,20 @@ describe Projects::StarrersController do
       end
     end
 
+    context 'N+1 queries' do
+      render_views
+
+      it 'avoids N+1s loading users', :request_store do
+        get_starrers
+
+        control_count = ActiveRecord::QueryRecorder.new { get_starrers }.count
+
+        create_list(:user, 5).each { |user| user.toggle_star(project) }
+
+        expect { get_starrers }.not_to exceed_query_limit(control_count)
+      end
+    end
+
     context 'when project is public' do
       before do
         project.update_attribute(:visibility_level, Project::PUBLIC)